nested 循环

循环可以嵌套在另一个循环中。 C ++允许至少256级嵌套。

语法 (Syntax)

C ++中nested for loop语句的语法如下 -

for ( init; condition; increment ) {
   for ( init; condition; increment ) {
      statement(s);
   }
   statement(s); // you can put more statements.
}

C ++中nested while loop语句的语法如下 -

while(condition) {
   while(condition) {
      statement(s);
   }
   statement(s); // you can put more statements.
}

C ++中nested do...while loop语句的语法如下 -

do {
   statement(s); // you can put more statements.
   do {
      statement(s);
   } while( condition );
} while( condition );

例子 (Example)

以下程序使用嵌套for循环来查找从2到100的素数 -

#include <iostream>
using namespace std;
int main () {
   int i, j;
   for(i = 2; i<100; i++) {
      for(j = 2; j <= (i/j); j++)
         if(!(i%j)) break; // if factor found, not prime
         if(j > (i/j)) cout << i << " is prime\n";
   }
   return 0;
}

这会产生以下结果 -

2 is prime
3 is prime
5 is prime
7 is prime
11 is prime
13 is prime
17 is prime
19 is prime
23 is prime
29 is prime
31 is prime
37 is prime
41 is prime
43 is prime
47 is prime
53 is prime
59 is prime
61 is prime
67 is prime
71 is prime
73 is prime
79 is prime
83 is prime
89 is prime
97 is prime